Influence of CO 2 Curing and Autoclaved Aerated Concrete Powder on Sulfate Attack of Cement Paste at Low Temperature

This paper studied the influence of CO2 curing and autoclaved aerated concrete powder on the sulfate attack of a cement sample at low temperature. The basic performance including compressive strength, mass and volume changes, and microstructure tests were analyzed by X-ray diffraction (QXRD/Rietveld), mercury intrusion porosimeter (MIP) and scanning electron microscope-energy dispersive spectrometer (SEM-EDS) analysis. Results proved that the strength of PC (Portland cement)-WAAC (waste autoclaved aerated concrete) pastes decreased after low-temperature sulfate attack; however, carbonation curing could mitigate the decrease. Compared with the strength of the uncarbonated specimens without sulfate immersion, the strengths of the CO2-cured specimens added with 0%, 10%, and 20% of WAAC after 6 months of sulfate immersion were still 3.93%, 11.90%, and 18.31% higher. The compressive strength reduction of the carbonated samples after 6 months of low-temperature sulfate immersion (9.31%-46.15%) was much lower than that of the uncarbonated specimens (15.55%-61.97%). In addition, CO2 curing decreased the porosity and improved the pore structure of the samples, thereby inhibiting sample volume expansion resulting from sulfate immersion. Carbonation curing improved the resistance of PC-WAAC specimens to low-temperature sulfate attack. After low-temperature sulfate immersion, thaumasite did not form in the carbonation curing samples. Therefore, WAAC recycling combined with carbonation curing can produce cementitious materials with good environmental sustainability and better long-term durability in sulfate erosion areas.